1. Field of the Invention
The present invention relates to an ultrasonic coding modem for digital network communication by means of using transmitting- and receiving devices, of which each includes a piezoelectric substrate and an interdigital transducer (IDT) having a coded pattern. The coded pattern of the IDT in the transmitting device is in reverse to that in the receiving device.
2. Description of the Prior Art
In recent years, digitalization techniques on telegraphic communication are in rapid progress. A code division multiple access (CDMA) method is, more especially, powerful for making a transmission speed high in spread spectrum communication. If the CDMA method has a surface acoustic wave (SAW) matched filter, it is possible to make the transmission speed still higher. However, it is difficult for a conventional type of CDMA method with the SAW matched filter to realize a base-band communication because of a coded message-signal in condition of a phase shift keying (PSK) burst-signal. In other words, it is necessary to transduce the PSK burst-signal to a digital pulse signal with a high speed for the base-band communication. In order to make the digital pulse signal, the use of a complicated circuit is unavoidable for the conventional type of CDMA method with the SAW matched filter.
An object of the present invention is to provide an ultrasonic coding modem for digital network communication comprising a transmitting device and a receiving device.
Another object of the present invention is to provide the transmitting device capable of coding a message digital-signal applied thereto, and delivering a coded digital-signal into a digital network.
Another object of the present invention is to provide the receiving device capable of receiving the coded digital-signal from the digital network, and detecting an output digital-signal corresponding to the message digital-signal.
Another object of the present invention is to provide an ultrasonic coding modem for digital network communication capable of making the coded digital-signal, in the digital network, play a role as a pseudo noise to keep a base-band communication secret.
Another object of the present invention is to provide the transmitting- and receiving devices capable of recognizing each other in the digital network.
Another object of the present invention is to provide an ultrasonic coding modem for digital network communication capable of a low electric power consumption.
Another object of the present invention is to provide an ultrasonic coding modem for digital network communication excellent in durability and manufacturing.
A still other object of the present invention is to provide an ultrasonic coding modem for digital network communication having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided an ultrasonic coding modem for digital network communication comprising a transmitting device and a receiving device. The transmitting device consists of an input terminal, a first piezoelectric substrate, an input IDT consisting of at least three interdigital electrode pairs, a first intermediary IDT, an electrode group, a synchronizing device, an envelope detecting device, and an output terminal. The receiving device consists of a receiving terminal, a second piezoelectric substrate, a second intermediary IDT, an output IDT, and a detecting terminal. The input IDT having a coded pattern, the first intermediary IDT, and the electrode group are formed on the first piezoelectric substrate. The electrode group consists of two IDTs and a central IDT between the two IDTs. The synchronizing device is connected between the first intermediary IDT and one of the two IDTs of the electrode group. The envelope detecting device is connected with the central IDT of the electrode group. The output IDT has a coded pattern in reverse to the input IDT. The second intermediary IDT and the output IDT are formed on the second piezoelectric substrate.
When a pulse (1) of a message digital-signal is applied to the input IDT via the input terminal, a SAW is excited on the first piezoelectric substrate, and then, a coded burst-signal corresponding to the SAW is detected at the first intermediary IDT. The coded burst-signal arrives at the two IDTs of the electrode group simultaneously, and two SAWs are excited on the first piezoelectric substrate, respectively. When the two SAWs are transmitted to the envelope detecting device via the central IDT of the electrode group, a coded digital-signal occurs. Thus, the coded digital-signal is delivered from the output terminal into a digital network. On the other hand, if the coded digital-signal is received at the second intermediary IDT via the receiving terminal from the digital network, a SAW is excited on the second piezoelectric substrate. In this time, the SAW excited at the second intermediary IDT corresponds to the SAW excited at the input IDT, a decoded pulse (1) is detected at the output IDT. Thus, an output digital-signal, which is composed of the decoded pulse (1) and no detected pulse (0), and is equivalent to the message digital-signal, is delivered at the detecting terminal.
According to another aspect of the present invention there are provided input- and output IDTs, of which coded patterns are changed in accordance with a designated time region, respectively.
According to another aspect of the present invention there is provided a transmitting device, wherein a transmitting direction of the SAW excited at the input IDT is orthogonal to that of the two SAWs excited at the two IDTs of the electrode group.
According to another aspect of the present invention there are provided first- and second piezoelectric substrates made of a piezoelectric ceramic, respectively, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there are provided first- and second input IDTs in place of the input IDT, and first-and second output IDTs in place of the output IDT. The first input IDT consists of at least three interdigital electrode pairs, and has one coded pattern. The second input IDT consists of at least three interdigital electrode pairs, and has another coded pattern. The first output IDT has a coded pattern in reverse to the first input IDT. The second output IDT has a coded pattern in reverse to the second input IDT.
When pulses (0 and 1) of a message digital-signal are applied to the first- and second input IDTs, respectively, via the input terminal, first- and second SAWs are excited on the first piezoelectric substrate. And then, a coded burst-signal corresponding to the first- and second SAWs, respectively, is detected at the first intermediary IDT. The coded burst-signal arrives at the two IDTs of the electrode group simultaneously, and third- and fourth SAWs are excited on the first piezoelectric substrate, respectively. When the third- and fourth SAWs are transmitted to the envelope detecting device via the central IDT of the electrode group, a coded digital-signal occurs. Thus, the coded digital-signal is delivered from the output terminal into a digital network. On the other hand, if the coded digital-signal is received at the second intermediary IDT via the receiving terminal from the digital network, a fifth SAW is excited on the second piezoelectric substrate. In this time, the fifth SAW corresponds to the first- and second SAWs, respectively, decoded pulses (0 and 1) are detected at the first- and second output IDTs, respectively. Thus, an output digital-signal, which is based on the decoded pulses (0 and 1) and is equivalent to the message digital-signal, is delivered at the detecting terminal.
According to another aspect of the present invention there are provided first- and second input IDTs, of which each coded pattern is changed in accordance with a designated time region, and in the same time, first- and second output IDTs, of which each coded pattern is changed in accordance with a designated time region.
According to other aspect of the present invention there is provided a transmitting device, wherein a transmitting direction of the first- and second SAWs is orthogonal to that of the third- and fourth SAWs.
According to a further aspect of the present invention there is provided a third input IDT, by which the first- and second input IDTs are replaced. The third input IDT has two coded patterns, which are exchanged from each other in response to the pulses (0 and 1) of the message digital-signal applied to the input IDT.